sister fucked by NOT her younger step-brother

We are a group of women and we all live at or play in a TRAILER PARK where anything goes and everyone CUMS!! We have sex in public, on the street, in the ally and our swingers parties are the BEST in the STATE!

she has the most beautiful wet pussy , love to eat her first ,MMMMMMMMMMMMMit should be a sin not too ,MMMMMMMMM, she is so sexy and so juicy and tight ,MMMMMMMMMMMMM, I would have to pull out from time to time and suck her pussy juicies and lick her clit , then go back to fucken ,love the way she sucks him clean ,MMMMMMMMMMMM, she is a 10 ,

I don't understand the title. Why emphasize that he is 'NOT' her step-brother? Wouldn't it make more sense to say who he is to her, rather than who he is specifically not?

Also, the title begins with the word 'sister', so whose sister is she? Taken literally, the title seems to say that she is his sister, not his step-sister, in which case, if they are blood siblings, why not state that instead of specifying that they are not step-siblings?